U.S. patent application number 13/493164 was filed with the patent office on 2012-11-15 for power transmitting device, power receiving device, and power transmission system.
This patent application is currently assigned to MURATA MANUFACTURING CO., LTD. Invention is credited to Henri Bondar, Keiichi Ichikawa.
Application Number | 20120286583 13/493164 |
Document ID | / |
Family ID | 47141400 |
Filed Date | 2012-11-15 |
United States Patent
Application |
20120286583 |
Kind Code |
A1 |
Ichikawa; Keiichi ; et
al. |
November 15, 2012 |
Power Transmitting Device, Power Receiving Device, and Power
Transmission System
Abstract
A power transmission system that includes a power transmitting
device and a power receiving device. The power transmitting device
includes a high-frequency voltage generator, a piezoelectric
resonator, a power transmitting device side passive electrode, and
a power transmitting device side active electrode. The power
receiving device includes a piezoelectric resonator, a load, a
power receiving device side passive electrode, and a power
receiving device side active electrode. The active electrode of the
power transmitting device and the active electrode of the power
receiving device are in proximity with each other, whereby the
power transmitting device and the power receiving device are
capacitively coupled through the active electrodes and the
surrounding dielectric medium.
Inventors: |
Ichikawa; Keiichi;
(Nagaokakyo-shi, JP) ; Bondar; Henri; (Kyoto-shi,
JP) |
Assignee: |
MURATA MANUFACTURING CO.,
LTD
Nagaokakyo-shi
JP
|
Family ID: |
47141400 |
Appl. No.: |
13/493164 |
Filed: |
June 11, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2011/002664 |
May 13, 2011 |
|
|
|
13493164 |
|
|
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Current U.S.
Class: |
307/104 |
Current CPC
Class: |
H02J 50/05 20160201;
H01L 41/107 20130101; H02J 5/005 20130101; H02J 50/70 20160201 |
Class at
Publication: |
307/104 |
International
Class: |
H02J 17/00 20060101
H02J017/00 |
Claims
1. A power transmitting device comprising: a power transmitting
device side active electrode; a power transmitting device side
passive electrode; and a high-frequency voltage generating circuit
connected between the power transmitting device side active
electrode and the power transmitting side passive electrode,
wherein the high-frequency voltage generating circuit includes a
step-up circuit having an LC resonant circuit, and wherein an
inductor of the LC resonant circuit is a piezoelectric device.
2. The power transmitting device according to claim 1, wherein a
capacitor of the LC resonant circuit has a capacitance that
corresponds to a capacitance generated between the power
transmitting device side active electrode and the power
transmitting side passive electrode.
3. The power transmitting device according to claim 1, wherein the
piezoelectric device is configured so as to be inductive at a
frequency of a voltage generated by the high-frequency voltage
generating circuit.
4. The power transmitting device according to claim 1, wherein the
piezoelectric device is a piezoelectric resonator or a
piezoelectric transformer.
5. The power transmitting device according to claim 1, wherein the
step-up circuit includes a voltage transforming circuit.
6. The power transmitting device according to claim 1, wherein the
high-frequency voltage generating circuit is configured to tune a
resonant frequency of the piezoelectric device.
7. A power receiving device comprising: a power receiving device
side active electrode; a power receiving device side passive
electrode; and a load circuit connected between the power receiving
device side active electrode and the power receiving side passive
electrode, wherein the load circuit includes a step-down circuit
having an LC resonant circuit, and wherein an inductor of the LC
resonant circuit is a piezoelectric device.
8. The power receiving device according to claim 7, wherein a
capacitor of the LC resonant circuit has a capacitance that
corresponds to a capacitance generated between the power receiving
device side active electrode and the power receiving side passive
electrode
9. The power receiving device according to claim 7, wherein the
piezoelectric device is configured so as to be inductive at a
frequency of a voltage input to the load circuit.
10. The power receiving device according to claim 7, wherein the
piezoelectric device is a piezoelectric resonator or a
piezoelectric transformer.
11. The power receiving device according to claim 7, wherein the
step-down circuit includes a voltage transforming circuit.
12. A power transmission system comprising: a power transmitting
device according to claim 1; and a power receiving device
including: a power receiving device side active electrode; a power
receiving device side passive electrode; and a load circuit
connected between the power receiving device side active electrode
and the power receiving side passive electrode.
13. A power transmission system comprising: a power transmitting
device including: a power transmitting device side active
electrode; a power transmitting device side passive electrode; and
a high-frequency voltage generating circuit connected between the
power transmitting device side active electrode and the power
transmitting side passive electrode; and a power receiving device
according to claim 7.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of International
application No. PCT/JP2011/002664, filed May 13, 2011, the entire
content of which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to power transmitting devices,
power receiving devices, and power transmission systems which
transmit electric power in a noncontact manner.
BACKGROUND OF THE INVENTION
[0003] PTL 1 discloses a system configured to transmit electric
power through capacitive coupling.
[0004] The power transmission system described in PTL 1 includes: a
power transmitting device including a high-frequency high-voltage
generator, generating electrodes to define the couple of generator
active/passive electrodes; a power receiving device including a
high-frequency high-voltage load, and electromotive electrodes to
define the load side active/passive pair.
[0005] A voltage lower than that applied to the active electrode is
applied to the passive electrode among the generating electrodes,
and a voltage lower than that applied to the active electrode is
applied to the passive electrode among the electromotive
electrodes.
[0006] The high-frequency voltage used in this system has a
frequency ranging from 10 kHz to 10 MHz and a voltage ranging from
100 V to 10 kV. When the frequency of the high-frequency voltage is
within this range, the device does not radiate energy in the form
of electromagnetic waves, and an electrostatic field is generated
in a surrounding medium because the wavelength(lambda) in the
surrounding medium is large enough relative to the size D of the
device, or D<<(lambda).
[0007] FIG. 1 illustrates the basic configuration of the power
transmission system of PTL 1. The power transmitting device
includes a high-frequency high-voltage generator 1, a passive
electrode 2, and an active electrode 3. The power receiving device
includes a high-frequency high-voltage load 5, a passive electrode
7, and an active electrode 6. The active electrode 3 of the power
transmitting device and the active electrode 6 of the power
receiving device are located in proximity to each other and are
surrounded by a high electric field area 4 the power transmitting
device and the power receiving device are capacitively coupled
through the generating and electromotive electrodes and the
surrounding dielectric medium. [0008] [PTL 1] National Publication
of International Patent Application No. 2009-531009
SUMMARY OF THE INVENTION
[0009] In a power transmission system, such as the one described in
PTL 1, configured to transmit electric power through capacitive
coupling from a power transmitting device to a power receiving
device, a high voltage at high frequency is required to increase
power transmission efficiency. Hence, a step-up circuit is provided
on the power transmitting device side and a step-down circuit is
provided on the power receiving device side. Usually, wire-wound
transformers are used as the step-up circuit and step-down circuit,
and the electrode's structure leads to an equivalent capacitor
connected in parallel with the secondary winding of the wire-wound
transformer. In this configuration, a circuit formed of the
capacitance of the resonant capacitor and the leakage inductance on
the secondary side of the wire-wound transformer resonates and
functions as a step-up circuit.
[0010] However, a wire-wound transformer has a size large enough to
provide the required inductance, and hence it is difficult to
decrease its height. It can be said that a wire-wound transformer
has a very large size compared with other general electronic
components. In addition, undesirable coupling between the
wire-wound transformer and other circuits is likely to be
generated. In the case of a resonant leakage wire-wound transformer
in particular, there is a large amount of leakage magnetic flux.
These factors result in a restricted arrangement of the wire-wound
transformer and an increased size of the whole device.
[0011] Further, when the wire-wound transformer is not efficiently
shielded, the coil performance (Q factor) thereof is strongly
affected by the nearby conductive materials.
[0012] Accordingly, it is an object of the present invention to
provide a power transmitting device, a power receiving device, and
a power transmission system which are small and lightweight,
avoiding the above-described problems caused by the use of a
wire-wound transformer.
[0013] A power transmitting device according to the present
invention is configured to include: a power transmitting device
side active electrode; a power transmitting device side passive
electrode; and a high-frequency high-voltage generating circuit
connected between the power transmitting device side active
electrode and the power transmitting side passive electrode. The
high-frequency high-voltage generating circuit includes a step-up
circuit having an LC resonant circuit, and an inductor of the LC
resonant circuit is formed of a piezoelectric device.
[0014] A power receiving device according to the present invention
is configured to include: a power receiving device side active
electrode; a power receiving device side passive electrode; and a
load circuit connected between the power receiving device side
active electrode and the power receiving side passive electrode.
The load circuit includes a step-down circuit having an LC resonant
circuit, and an inductor of the LC resonant circuit is formed of a
piezoelectric device.
[0015] A power transmission system according to the present
invention is configured such that the power transmitting device and
the power receiving device are capacitively coupled through the
generating and electromotive electrodes and the surrounding
dielectric medium.
[0016] According to the present invention, the whole device is
reduced in size and leakage of magnetic flux is prevented. In
addition, transmission efficiency is increased.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 illustrates the basic configuration of the power
transmission system described in PTL 1.
[0018] FIG. 2A is a circuit diagram of a uncoupled power
transmitting device 101 according to a first embodiment; FIG. 2B is
an equivalent circuit of a piezoelectric resonator 21; and FIG. 2C
is an equivalent circuit of the power transmitting device 101
according to the first embodiment for the case where the frequency
of a voltage generated by a high-frequency voltage generator 11 is
a frequency in the frequency range from a resonant frequency fr to
an anti-resonant frequency fa.
[0019] FIG. 3 is a graph illustrating the frequency characteristics
of the impedance and phase of the piezoelectric resonator 21.
[0020] FIG. 4A is a circuit diagram of a uncoupled power receiving
device 201 according to a second embodiment; FIG. 4B is an
equivalent circuit of a piezoelectric resonator 22; and FIG. 4C is
an equivalent circuit of the power receiving device 201 according
to the second embodiment for the case where the frequency of a
voltage received through the capacitive coupling of a capacitor C2
is a frequency in the frequency range from the resonant frequency
fr to the anti-resonant frequency fa illustrated in FIG. 3.
[0021] FIG. 5 is a circuit diagram of a power transmission system
301 according to a third embodiment. The coupling coefficient k and
the two capacitances C1 and C2 are a representation of the
resulting electrostatic coupling between the system of
electrodes.
[0022] FIG. 6 illustrates an exemplary configuration of the power
transmission system 301 with a longitudinal open ends
representation.
[0023] FIG. 7 is a schematic sectional view of the power
transmission system 301 according to the third embodiment.
[0024] FIG. 8A is a circuit diagram of a power transmitting device
102 according to a fourth embodiment; FIG. 8B is an equivalent
circuit of a piezoelectric resonator 21; and FIG. 8C is an
equivalent circuit of the power transmitting device 102 according
to the fourth embodiment for the case where the frequency of a
voltage generated by a high-frequency voltage generator 11 is a
frequency in the frequency range from a resonant frequency fr to an
anti-resonant frequency fa.
[0025] FIG. 9A is a circuit diagram of a power receiving device 202
according to a fifth embodiment; FIG. 9B is an equivalent circuit
of a piezoelectric resonator 22; and FIG. 9C is an equivalent
circuit of the power receiving device 202 according to the fifth
embodiment for the case where the frequency of a voltage received
through the capacitive coupling of a capacitor C2 is a frequency in
the frequency range from the resonant frequency fr to the
anti-resonant frequency fa illustrated in FIG. 3.
[0026] FIG. 10 is a circuit diagram of a power transmission system
302 according to a sixth embodiment.
[0027] FIG. 11A is a circuit diagram of a power transmission system
303 according to a seventh embodiment, and FIG. 11B is its
equivalent circuit.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
[0028] A power transmitting device according to a first embodiment
will be described with reference to FIGS. 2A to 2C and FIG. 3.
[0029] FIG. 2A is a circuit diagram of a uncoupled power
transmitting device 101 according to the first embodiment. The
power transmitting device 101 includes a high-frequency voltage
generator 11, and a piezoelectric resonator 21. The equivalent
capacitor C1 represents the capacitance obtained between the two
generating electrodes when no receiving device is present. The
piezoelectric resonator 21 and the capacitor C1 are connected in
series to the high-frequency voltage generator 11.
[0030] FIG. 2B is an equivalent circuit of the piezoelectric
resonator 21. FIG. 3 is a graph illustrating the frequency
characteristics of the impedance and phase of the piezoelectric
resonator 21. In FIG. 3, a logarithmic scale is used for the
impedance axis (vertical axis), and a linear scale is used for the
frequency axis (horizontal axis). The piezoelectric resonator 21 is
represented by a parallel circuit formed of a capacitor Co and a
series circuit formed of an inductor L1 and a capacitor C11. The
capacitor C11 represents equivalent compliance corresponding to the
elastic force of a mechanical spring or rubber. The inductor L1
represents equivalent inductance corresponding to mechanical
inertial force (mass or moment). The capacitor Co corresponds to
the capacitance (parallel equivalent capacitance) between
electrodes. The piezoelectric resonator 21 is formed of a pair of
electrodes formed on the surface of a piezoelectric substrate. The
piezoelectric substrate has been subjected to poling treatment.
Hence, in the piezoelectric resonator 21, series resonance having a
resonant frequency fr based on the inductor L1 and the capacitor
C11 is generated, and parallel resonance having an anti-resonant
frequency fa mainly based on the capacitor Co and the inductor L1
is generated. The anti-resonant frequency fa is higher than the
resonant frequency fr. In the frequency range between the resonant
frequency fr and the anti-resonant frequency fa, the inductance of
the inductor L1 becomes the dominant component of the impedance of
the piezoelectric resonator 21. In other words, referring to FIG.
3, the piezoelectric resonator 21 has inductive impedance, for
which the phase is positive, in the frequency range between the
resonant frequency fr and the anti-resonant frequency fa, and
equivalently works as an inductor. For frequencies below the
resonant frequency fr or above the anti-resonant frequency fa, the
piezoelectric resonator 21 has capacitive impedance, for which the
phase is negative, and equivalently works as a capacitor.
[0031] FIG. 2C is an equivalent circuit of the power transmitting
device 101 according to the first embodiment for the case where the
frequency of a voltage generated by the high-frequency voltage
generator 11 is a frequency in the frequency range from the
resonant frequency fr to the anti-resonant frequency fa. The
resonant frequency of an LC resonant circuit formed of the
capacitor C1 and the inductor L1 is set to be the frequency of the
high-frequency voltage generated by the high-frequency voltage
generator 11. As a result, the circuit illustrated in FIG. 2C works
as a step-up circuit.
[0032] According to the power transmitting device of the first
embodiment, the device can be reduced in size and leakage of
magnetic flux can be reduced, compared with the case in which the
inductor L1 illustrated in FIG. 2C is formed of a magnetic core and
a winding.
[0033] Piezoelectric devices including a piezoelectric resonator
have a high Q factor compared with coils of wire. Hence, when a
piezoelectric device is used as an inductor, transmission
efficiency can be increased.
Second Embodiment
[0034] FIG. 4A is a circuit diagram of an uncoupled power receiving
device 201 according to a second embodiment. The power receiving
device 201 includes a piezoelectric resonator 22, and a load RL.
The equivalent capacitor C2 represents the capacitance obtained
between the two electromotive electrodes when no power transmitting
device is present. The piezoelectric resonator 22 and the load RL
is connected in series to the capacitor C2.
[0035] FIG. 4B is an equivalent circuit of the piezoelectric
resonator 22. As illustrated in FIG. 4B, the piezoelectric
resonator 22 is represented by a parallel circuit formed of a
capacitor Co and a series circuit formed of an inductor L2 and a
capacitor C21. This equivalent circuit is similar to the one
illustrated in FIG. 2B in the first embodiment, and has frequency
characteristics similar to those illustrated in FIG. 3.
[0036] FIG. 4C is an equivalent circuit of the power receiving
device 201 according to the second embodiment for the case where
the frequency of a voltage received through a capacitive coupling
involving C2 is a frequency in the frequency range from the
resonant frequency fr to the anti-resonant frequency fa illustrated
in FIG. 3. The resonant frequency of an LC resonant circuit formed
of the inductor L2 and the capacitor C2 is equal to the frequency
of the voltage received through the capacitive coupling. The
circuit illustrated in FIG. 4C works as a step-down circuit when
coupled to a power transmitting device.
[0037] According to the power receiving device of the second
embodiment, the device can be reduced in size and leakage of
magnetic flux can be reduced, compared with the case in which the
inductor L2 illustrated in FIG. 4C is formed of a magnetic core and
a winding.
Third Embodiment
[0038] All the electrodes are interacting through a dielectric
medium (including air and vacuum). The quasi static-situation
(negligible far field radiation) in case of four electrodes (one
generator, one load), is fully described by a 4.times.4 matrix
involving 10 different capacitive coefficients. In case of a two
port representation of the system, the power transfer is fully
described in the classical circuit frame by two coupled equivalent
capacitors C1 and C2 and a mutual capacitance CM or equivalently a
coupling factor k. These values can be derived from the 10
independent general coefficients of the original matrix and will be
referred in the following as the two-port three-coefficient
coupling model.
[0039] In some practical situations the behavior is dominated by
some specific coefficients among the many involved, for instance
the coupling coefficients between on one hand the active electrodes
and on the other hand the passive ones.
[0040] FIG. 5 is a circuit diagram of a power transmission system
301 according to a third embodiment. The power transmission system
301 is formed of the power transmitting device 101 described in the
first embodiment and the power receiving device 201 described in
the second embodiment. The capacitor C1 of the power transmitting
device 101 is coupled to the capacitor C2 of the power receiving
device 201 according to the two port model for energy transport,
whereby electric power is transmitted from the power transmitting
device 101 to the power receiving device 201 through an electric
field.
[0041] Here, mutual capacitance CM and a coupling factor k have the
following relation.
k=CM/SQRT(C1*C2)
[0042] FIG. 6 illustrates an exemplary configuration of the power
transmission system 301 with a longitudinal open ends
representation. The power transmitting device 101 includes the
high-frequency voltage generator 11, a piezoelectric resonator 21,
a power transmitting device side passive electrode 2, and a power
transmitting device side active electrode 3. The power receiving
device 201 includes a piezoelectric resonator 22, a load RL, a
power receiving device side passive electrode 7, and a power
receiving device side active electrode 6. The active electrode 3 of
the power transmitting device 101 and the active electrode 6 of the
power receiving device 201 are located in proximity to each other
and are surrounded by a high electric field area 4, the power
transmitting device and the power receiving device are capacitively
coupled through the generating and electromotive electrodes and the
surrounding dielectric medium.
[0043] FIG. 7 is a schematic sectional view of the power
transmission system 301 according to the third embodiment. In this
example, the passive electrode 2 of the power transmitting device
101 faces to some extend the passive electrode 7 of the power
receiving device 201. The power transmitting device side active
electrode 3 and the transmitting device side passive electrode 2
which surrounds the active electrode 3 in an insulated state are
formed near the upper surface of the casing of the power
transmitting device 101. In addition, a high-frequency high-voltage
generating circuit 1 that applies a high-frequency voltage between
the active electrode 3 and the passive electrode 2 is provided
within the casing of the power transmitting device 101. The
high-frequency high-voltage generating circuit 1 is a circuit
formed of the high-frequency voltage generator 11, and the
piezoelectric resonator 21.
[0044] The casing of the power transmitting device 101 is a
single-piece plastic body made of, for example, an ABS resin,
formed in such a manner as to integrate the active electrode 3 and
the passive electrode 2 therein, whereby the outer surface of the
casing has an insulation structure.
[0045] A power receiving device side active electrode 6 and the
power receiving device side passive electrode 7 which surrounds the
active electrode 6 in an insulated state are provided near the
lower surface of the casing of the power receiving device 201. In
addition, a load circuit 5 for electric power induced between the
active electrode 6 and the passive electrode 7 is provided within
the casing of the power receiving device 201. The load circuit 5 is
a circuit formed of the piezoelectric resonator 22, the wire-wound
transformer T2, and the load RL.
[0046] The casing of the power receiving device 201 is also a
single-piece plastic body made of, for example, an ABS resin,
formed in such a manner as to integrate the active electrode 6 and
the passive electrode 7 therein, whereby the outer surface of the
casing has an insulation structure.
[0047] The active electrode 3 of the power transmitting device 101
is shaped like a circle. The passive electrode 2 is provided with a
circular opening for the active electrode 3. In other words, the
passive electrode 2 is arranged so as to surround the active
electrode 3 in an insulated state. Also in the power receiving
device 201, the active electrode 6 is shaped like a circle, and the
passive electrode 7 is provided with a circular opening for the
active electrode 6. The passive electrode 7 is arranged so as to
surround the active electrode 6 in an insulated state.
Fourth Embodiment
[0048] When a voltage generated by the high-frequency voltage
generator 11 is low and there is strong coupling between a power
transmitting device and a power receiving device, there may be a
case in which a high voltage required for sufficient power
transmission is not obtained by stepping up the voltage due to the
resonance of the power transmitting device 101 described in the
first embodiment. In such a case, a wire-wound transformer T1 may
be provided in a stage prior to the piezoelectric resonator of the
power transmitting device, thereby increasing a voltage applied to
a piezoelectric resonator 21, as in a fourth embodiment described
below.
[0049] A power transmitting device according to a fourth embodiment
will be described with reference to FIGS. 8A to 8C.
[0050] FIG. 8A is a circuit diagram of a power transmitting device
102 according to the fourth embodiment. The power transmitting
device 102 includes a high-frequency voltage generator 11, a
wire-wound transformer T1, a piezoelectric resonator 21, and an
equivalent capacitor C1. The high-frequency voltage generator 11 is
connected to the primary side of the wire-wound transformer T1, and
a series circuit formed of the piezoelectric resonator 21 and the
capacitor C1 is connected to the secondary side of the wire-wound
transformer T1.
[0051] FIG. 8B is an equivalent circuit of the piezoelectric
resonator 21. The piezoelectric resonator 21 is represented by a
parallel circuit formed of a capacitor Co and a series circuit
formed of an inductor L1 and a capacitor C11. The capacitor C11
represents equivalent compliance corresponding to the elastic force
of a mechanical spring or rubber. The inductor L1 represents
equivalent inductance corresponding to mechanical inertial force
(mass or moment). The capacitor Co corresponds to the capacitance
(parallel equivalent capacitance) between electrodes. The
piezoelectric resonator 21 is formed of a pair of electrodes formed
on the surface of a piezoelectric substrate. The piezoelectric
substrate has been subjected to poling treatment. Hence, in the
piezoelectric resonator 21, series resonance having a resonant
frequency fr based on the inductor L1 and the capacitor C11 is
generated, and parallel resonance having an anti-resonant frequency
fa mainly based on the capacitor Co and the inductor L1 is
generated. The anti-resonant frequency fa is higher than the
resonant frequency fr. In the frequency range between the resonant
frequency fr and the anti-resonant frequency fa, the inductance of
the inductor L1 becomes the dominant component of the impedance of
the piezoelectric resonator 21. In other words, referring to FIG.
3, the piezoelectric resonator 21 has inductive impedance, for
which the phase is positive, in the frequency range between the
resonant frequency fr and the anti-resonant frequency fa, and
equivalently works as an inductor. For frequencies below the
resonant frequency fr or above the anti-resonant frequency fa, the
piezoelectric resonator 21 has capacitive impedance, for which the
phase is negative, and equivalently works as a capacitor.
[0052] FIG. 8C is an equivalent circuit of the power transmitting
device 102 according to the fourth embodiment for the case where
the frequency of a voltage generated by the high-frequency voltage
generator 11 is a frequency in the frequency range from the
resonant frequency fr to the anti-resonant frequency fa. The
resonant frequency of an LC resonant circuit formed of the
capacitor C1 and the inductor L1 (to be precise, an LC resonant
circuit formed of the capacitance of the capacitor C1 and the
combined inductance of the secondary side leakage inductance of the
wire-wound transformer T1 and the inductance of the inductor L1) is
set to be the frequency of the high-frequency voltage generated by
the high-frequency voltage generator 11. As a result, the
wire-wound transformer T1 and the LC resonant circuit work as a
step-up circuit. The numbers of turns of the primary and secondary
windings of the wire-wound transformer T1 are appropriately set so
as to realize the step-up ratio required to output a predetermined
high voltage to the capacitor C1. For example, the high-frequency
voltage generator 11 generates a high-frequency voltage of 5 to 12
V, which is stepped up to 50 to 240 V by the wire-wound transformer
T1.
[0053] According to the power transmitting device of the fourth
embodiment, the device can be reduced in size and leakage of
magnetic flux can be reduced, compared with the case in which the
inductor L1 illustrated in FIG. 8C is formed of a magnetic core and
a winding. In addition, the wire-wound transformer can be reduced
in size compared with the case in which the inductor L1 in the
equivalent circuit illustrated in FIG. 8C is formed of the
secondary side leakage inductance of the wire-wound
transformer.
[0054] Piezoelectric devices including a piezoelectric resonator
have a high Q factor compared with coils of wire. Hence, when a
piezoelectric device is used as an inductor, transmission
efficiency can be increased.
[0055] The wire-wound transformer T1 is preferably a closed
magnetic circuit wire-wound transformer such as a shell-type
transformer having a magnetic core arranged outside of the windings
and generating little leakage of an undesirable magnetic field, to
prevent leakage of undesirable magnetic flux.
[0056] In addition, the coupling coefficient of the wire-wound
transformer T1 is preferably high.
[0057] Further, the wire-wound transformer T1 may be omitted when
the high-frequency voltage generated by the high-frequency voltage
generator 11 is sufficiently high.
Fifth Embodiment
[0058] When a voltage generated by a power transmitting device is
low and there is strong coupling between a power receiving device
and the power transmitting device, there may be a case in which
sufficient power transmission is not realized by the voltage
step-down due to the resonance of the power receiving device 201
described in the second embodiment. In such a case, a wire-wound
transformer T2 may be provided in a stage subsequent to the
piezoelectric resonator of the power receiving device, thereby
obtaining a predetermined voltage using an appropriate step-down
ratio, as in a fifth embodiment described below.
[0059] FIG. 9A is a circuit diagram of a power receiving device 202
according to a fifth embodiment. The power receiving device 202
includes an equivalent capacitor C2, a piezoelectric resonator 22,
a wire-wound transformer T2, and a load RL. A series circuit formed
of the piezoelectric resonator 22 and the capacitor C2 is connected
to the primary side of the wire-wound transformer T2, and the load
RL is connected to the secondary side of the wire-wound transformer
T2.
[0060] FIG. 9B is an equivalent circuit of the piezoelectric
resonator 22. As illustrated in FIG. 9B, the piezoelectric
resonator 22 is represented by a parallel circuit formed of a
capacitor Co and a series circuit formed of an inductor L2 and a
capacitor C21. This equivalent circuit is similar to the one
illustrated in FIG. 2B in the first embodiment, and has frequency
characteristics similar to those illustrated in FIG. 3.
[0061] FIG. 9C is an equivalent circuit of the power receiving
device 202 according to the fifth embodiment for the case where the
frequency of a voltage received through the capacitive coupling via
C2 is a frequency in the frequency range from the resonant
frequency fr to the anti-resonant frequency fa illustrated in FIG.
3. The resonant frequency of an LC resonant circuit formed of the
inductor L2 and the capacitor C2 (to be precise, an LC resonant
circuit formed of the combined inductance of the primary side
leakage inductance of the wire-wound transformer T2 and the
inductance of the inductor L2 and the capacitance of the capacitor
C2) is set to be the frequency of the high-frequency voltage
received through the capacitive coupling via C2. As a result, the
wire-wound transformer T2 and the LC resonant circuit work as a
step-down circuit. The numbers of turns of the primary and
secondary windings of the wire-wound transformer T2 are
appropriately set so as to realize the step-down ratio required to
output a predetermined voltage to the load RL. For example, a
high-frequency voltage of 100 V to 3 kV is induced in the capacitor
C2, and the wire-wound transformer T2 steps down this voltage to 5
to 24 V.
[0062] According to the power receiving device of the fifth
embodiment, the device can be reduced in size and leakage of
magnetic flux can be reduced, compared with the case in which the
inductor L2 illustrated in FIG. 9C is formed of a magnetic core and
a winding. In addition, the wire-wound transformer can be reduced
in size compared with the case in which the inductor L2 in the
equivalent circuit illustrated in FIG. 9C is formed of the primary
side leakage inductance of the wire-wound transformer.
[0063] The wire-wound transformer T2 is preferably a closed
magnetic circuit wire-wound transformer such as an external-magnet
transformer having a magnetic core arranged outside of the windings
and generating little undesirable magnetic field, to prevent
leakage of undesirable magnetic flux.
Sixth Embodiment
[0064] FIG. 10 is a circuit diagram of a power transmission system
302 according to a sixth embodiment. The power transmission system
302 is formed of the power transmitting device 102 described in the
fourth embodiment and the power receiving device 202 described in
the fifth embodiment. The capacitor C1 of the power transmitting
device, the capacitor C2 of the power receiving device and the
coefficient k are the two port representation of the coupling
through a quasi-static electric field.
Seventh Embodiment
[0065] FIG. 11A is a circuit diagram of a power transmission system
303 according to a seventh embodiment, and FIG. 11B is its
equivalent circuit. The power transmission system 303 is formed of
a power transmitting device 103 and a power receiving device
203.
[0066] The power transmitting device 103 is formed of the
high-frequency voltage generator 11, a piezoelectric transformer
31, and the coupling capacitor C1. The power receiving device 203
is formed of the coupling capacitor C2, a piezoelectric transformer
32, and the load RL.
[0067] In the piezoelectric transformer 31, primary side electrodes
E11 and E12 and a secondary side electrode E20 are formed on a
piezoelectric ceramic substrate shaped like a rectangular
parallelepiped. The primary side of the piezoelectric substrate is
poled in a direction from the electrode E11 to the electrode E12.
The secondary side of the ceramic substrate is poled in a direction
from the electrodes E11 and E12 to an electrode E20. When a
high-frequency voltage is applied between the primary side
electrodes E11 and E12, the energy is converted into elastic energy
due to the primary side inverse piezoelectric effect, and the
elastic energy is converted back into electric energy due to the
secondary side piezoelectric effect.
[0068] As illustrated in FIG. 11B, the equivalent circuit of the
piezoelectric transformer 31 includes an ideal transformer T11,
capacitors C10, C11, and C12, and an inductor L11. The capacitors
C10 and C12 correspond to stray capacitance, and the capacitor C11
and the inductor L11 are electromechanical parameters. The resonant
frequency of the piezoelectric transformer 31 is mainly determined
by the resonance of a resonance circuit formed of the capacitor C11
and the inductor L11. Since the conversion of electric energy is
performed through elastic oscillation, a frequency near the
characteristic resonant frequency determined by the elastic wave
propagation velocity and dimensions of the piezoelectric ceramic
substrate is used. In other words, the frequency of a
high-frequency voltage generated by the high-frequency voltage
generator 11 is set to be near the resonant frequency of the
piezoelectric transformer 31.
[0069] The piezoelectric transformer 32 has basically the same
configuration as the piezoelectric transformer 31. However, the
relationship between the primary and the secondary sides is
reversed. That is, energy is input to the piezoelectric transformer
32 from the electrode E20, which is generally on the secondary
side, and energy is output from the electrodes E11 and E12, which
are generally on the primary side.
[0070] As illustrated in FIG. 11B, the equivalent circuit of the
piezoelectric transformer 32 includes an ideal transformer T21,
capacitors C20, C21, and C22, and an inductor L21. The capacitors
C20 and C22 correspond to stray capacitance, and the capacitor C21
and the inductor L21 are electromechanical parameters. The resonant
frequency of the piezoelectric transformer 32 is mainly determined
by the resonance of a resonance circuit formed of the capacitor C21
and the inductor L21. When a voltage induced in the capacitor C2 is
applied to the electrode E20, its energy is converted into elastic
energy due to the secondary side inverse piezoelectric effect, and
the elastic energy is converted back into electric energy due to
the primary side piezoelectric effect. The frequency of a
high-frequency voltage generated by the high-frequency voltage
generator 11 is set to be the resonant frequency of the
piezoelectric transformer 32.
[0071] For example, the high-frequency voltage generator 11
generates a high-frequency voltage of 5 to 12 V, and the
piezoelectric transformer 31 steps up this voltage to 100 V to 3
kV. The piezoelectric transformer 32 steps down the voltage of 100
V to 3 kV induced in the capacitor C2 to 5 to 12 V, and outputs the
stepped-down voltage to the load RL.
[0072] In this manner, by using a piezoelectric transformer as a
step-up circuit, the power transmitting device can be reduced in
size and leakage of magnetic flux can be prevented, compared with
the case of using a step-up wire-wound transformer.
[0073] In addition, by using a piezoelectric transformer, which is
usually used as a step-up transformer, as a step-down transformer
in a power receiving device, the power receiving device can be
reduced in size and leakage of magnetic flux can be prevented,
compared with the case of using a step-down wire-wound
transformer.
Eighth Embodiment
[0074] The very high internal Q factors of piezoelectric materials
(compared with usual coils) imply satisfaction of the conditions
for very sharp frequency tuning between the two tuned circuits.
When a continuous voltage, in addition to an oscillating voltage,
is applied across the primary electrodes, this voltage generates a
continuous strain inside the material, allowing the resonant
frequency to be slightly changed. Hence, tuning is possible with
only a small effect on the Q factor. This tuning technique may be
used to adapt the device to various coupling conditions between the
power transmitting device and power receiving device. In other
embodiments mechanical or purely electrical means, such as
adjustable capacitors or inductors, are used.
Other Embodiments
[0075] While examples in which the load RL is an AC load have been
shown in the embodiments described above, the present invention may
be applied to the case of a DC load by providing a rectifying and
smoothing circuit.
[0076] Wire-wound transformers are used both in the power
transmitting device 102 and the power receiving device 202 in the
fourth embodiment, and piezoelectric transformers are used both in
the power transmitting device 103 and the power receiving device
203 in the fifth embodiment. However, by providing a wire-wound
transformer in one of a power transmitting device and a power
receiving device, a piezoelectric resonator or a piezoelectric
transformer may be provided in the other.
[0077] Further, a piezoelectric transformer may be combined with a
voltage transforming circuit. For example, in the power
transmitting device, when a sufficient step-up ratio is not
obtained by a piezoelectric transformer alone, or when a sufficient
step-up ratio is not obtained by a wire-wound transformer alone,
the piezoelectric transformer may be configured to be driven by a
voltage which has been stepped-up by the wire-wound transformer.
Similarly, in the power receiving device, when a sufficient
step-down ratio is not obtained by a piezoelectric transformer
alone, or when a sufficient step-down ratio is not obtained by a
wire-wound transformer alone, the wire-wound transformer may be
configured to further step-down a voltage which has been
stepped-down by the piezoelectric transformer. Through such
combination, impedance matching can be realized between a
high-impedance capacitive coupling portion and a low-impedance
high-frequency voltage generating circuit, or between a
high-impedance capacitive coupling portion and a low-impedance
load.
REFERENCE SIGNS LIST
[0078] C1, C2 . . . capacitors [0079] C10, C11, C12 . . .
capacitors [0080] C20, C21, C22 . . . capacitors [0081] Co . . .
capacitor [0082] E11, E12 . . . primary side electrodes [0083] E20
. . . secondary side electrode [0084] L1 . . . inductor [0085] L11
. . . inductor [0086] L2 . . . inductor [0087] L21 . . . inductor
[0088] RL . . . load [0089] T1 . . . wire-wound transformer [0090]
T11 . . . ideal transformer [0091] T2 . . . wire-wound transformer
[0092] T21 . . . ideal transformer [0093] 1 . . . high-frequency
high-voltage generating circuit [0094] 2 . . . power transmitting
device side passive electrode [0095] 3 . . . power transmitting
device side active electrode [0096] 5 . . . load circuit [0097] 6 .
. . power receiving device side active electrode [0098] 7 . . .
power receiving device side passive electrode [0099] 11 . . .
high-frequency voltage generator [0100] 21, 22 . . . piezoelectric
resonators [0101] 31, 32 . . . piezoelectric transformers [0102]
101, 102, 103 . . . power transmitting devices [0103] 201, 202, 203
. . . power receiving devices [0104] 301, 302, 303 . . . power
transmission systems
* * * * *